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EP1454923B1 - Process for preparation of thermally stable PVDF - Google Patents

Process for preparation of thermally stable PVDF Download PDF

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Publication number
EP1454923B1
EP1454923B1 EP04290393A EP04290393A EP1454923B1 EP 1454923 B1 EP1454923 B1 EP 1454923B1 EP 04290393 A EP04290393 A EP 04290393A EP 04290393 A EP04290393 A EP 04290393A EP 1454923 B1 EP1454923 B1 EP 1454923B1
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EP
European Patent Office
Prior art keywords
pvdf
optionally
dispersion
potassium
sodium acetate
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Expired - Lifetime
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EP04290393A
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German (de)
French (fr)
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EP1454923A1 (en
Inventor
Patrick Kappler
Véronique Gauthe
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Arkema France SA
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Arkema France SA
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/12—Powdering or granulating
    • C08J3/16—Powdering or granulating by coagulating dispersions
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M1/00—Substation equipment, e.g. for use by subscribers
    • H04M1/02—Constructional features of telephone sets
    • H04M1/0295—Mechanical mounting details of display modules
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F6/00—Post-polymerisation treatments
    • C08F6/24—Treatment of polymer suspensions
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/20—Compounding polymers with additives, e.g. colouring
    • C08J3/205—Compounding polymers with additives, e.g. colouring in the presence of a continuous liquid phase
    • C08J3/21—Compounding polymers with additives, e.g. colouring in the presence of a continuous liquid phase the polymer being premixed with a liquid phase
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/04—Oxygen-containing compounds
    • C08K5/09—Carboxylic acids; Metal salts thereof; Anhydrides thereof
    • C08K5/098—Metal salts of carboxylic acids
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
    • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
    • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
    • C08J2327/16—Homopolymers or copolymers of vinylidene fluoride

Definitions

  • PVDF polyvinylidene fluoride
  • the present invention relates to a process for manufacturing PVDF homopolymer or copolymer, more specifically a process by radical polymerization of vinylidene fluoride (VDF), and optionally a comonomer, in aqueous dispersion using a persulfate as initiator (also called initiator) .
  • VDF vinylidene fluoride
  • the polymerization is carried out optionally in the presence of a surfactant additive also called emulsifier or surfactant.
  • the PVDF dispersion obtained after the polymerization is washed, then sodium acetate and optionally potassium alkylsulphonate are added.
  • the PVDF obtained must contain as little as possible of this emulsifier and in general of the order of 300 ppm at most.
  • US Pat . No. 4,025,709 describes the polymerization of VDF in the presence of potassium persulfate as initiator, of sodium acetate and of a dispersing additive which may be a sodium perfluorooctanoate (ex 1-3) or a sulfonate of formula Rf-C 2 H 4 -SO 3 M wherein M denotes an alkali metal or ammonium.
  • a dispersing additive which may be a sodium perfluorooctanoate (ex 1-3) or a sulfonate of formula Rf-C 2 H 4 -SO 3 M wherein M denotes an alkali metal or ammonium.
  • the proportion of dispersing additive with respect to the PVDF formed is between 550 and 2200 ppm.
  • the PVDF is obtained in the form of a latex which is dried in an oven or separated by centrifugation to obtain PVDF. There is no washing of the latex, the PVDF thus contains between 550 and 2200
  • EP 169328 (US 4569978) describes the polymerization of VDF in the presence of Diisopropyl peroxydicarbonate (IPP) as initiator and there is no sodium acetate.
  • EP 816397 describes a process similar to the previous except that the initiator is di-tert-butyl peroxide.
  • EP 387938 describes the polymerization of VDF in the presence of ammonium persulfate as initiator, ethyl acetate as a chain transfer agent but without sodium acetate or dispersant additive.
  • US Pat . No. 5,555,556 describes the polymerization of VDF in the presence of an oxidizing-reducing pair but without dispersing additive or sodium acetate.
  • the oxidant may be a persulfate.
  • the PVDF manufactured according to the methods described above has insufficient thermal stability for applications that require extrusion, compression molding or injection molding.
  • Patent FR 1298572 describes PVDF containing salts of barium or strontium.
  • US Pat . No. 3,728,303 describes the polymerization of VDF in the presence of ammonium persulfate as an initiator but without any dispersant additive. Sodium or potassium chloride or chlorate is then added to the PVDF.
  • EP 870792 describes the polymerization of VDF in the presence of persulfate as initiator and a dispersant additive which is ammonium perfluorooctanoate. Potassium nitrate is added either during the polymerization of VDF or in PVDF before it is introduced into an extruder.
  • Patent Application BE 9600257 (US 5929152) describes the improvement of the stability of PVDF by the addition of a bismuth salt.
  • the application FR 2804438 describes a process for preparing a fluorinated polymer in aqueous emulsion in the presence of a fluorinated surfactant. The addition of sodium acetate is not suggested.
  • thermoly stable PVDF is obtained provided that the thermal stability does not occur. not degraded by unwanted residues of surfactant.
  • the polymerization is carried out optionally in the presence of a surfactant additive to increase the amount of PVDF produced per batch of polymerization but in this case the PVDF obtained must contain a residual surfactant additive level sufficiently low not to affect the thermal stability.
  • the content of the surfactant additive must be less than 300 ppm by weight relative to the PVDF to avoid a deterioration of the thermal stability.
  • the process is referred to as "emulsion", or any other process derived from the emulsion (microsuspension, miniemulsion, etc.) that can be carried out with persulfate as an initiator, which are well known in the art. skilled in the art.
  • emulsion or any other process derived from the emulsion (microsuspension, miniemulsion, etc.) that can be carried out with persulfate as an initiator, which are well known in the art. skilled in the art.
  • persulfate persulfate
  • the PVDF is separated from the water and any remains of the reagents involved.
  • the polymer is in the form of a latex composed of very fine particles, the average diameter of which is generally less than 1 micron.
  • This latex can be coagulated and optionally concentrated by removing a portion of the water for example by centrifugation.
  • Some surfactant additives that may be used in the polymerization may cause degradation of the thermal stability if they remain present in the PVDF.
  • the latex can be dried and simultaneously remove the surfactant by bringing it into contact with a hot gas in an atomizer and the PVDF powder is collected. This technique is known and used in PVDF manufacturing processes.
  • washing techniques are known per se.
  • a latex can be coagulated by adding salt and the water removed by centrifugation or filtration. This operation can be repeated after adding pure water.
  • the latex is diluted and then introduced into a coagulator or it is subjected to shearing in the presence of air. Under the cumulative effect of these two actions, the latex is transformed into aerated cream with a density lower than that of water.
  • This cream is optionally backwashed with deionized water, for example according to the process described in US Pat. No. 4,128,517. and EP 0 460 284. Washing with water makes it possible to rid the latex of the surfactant which was necessary for the polymerization or at least to greatly reduce its proportion relative to the PVDF.
  • the washed PDVF dispersion containing sodium acetate and sodium alkylsulfonate can be dried by any drying method. Spray drying or drying in a rotary dryer are particularly suitable.
  • the temperature chosen is the temperature sufficient to polymerize the VDF and is of the order of 45 to 130 ° C and advantageously between 70 and 90 ° C.
  • the desired pressure is of the order of 35 to 125 bars.
  • the volume of water in which the dispersion of the monomers is carried out, the amounts of dispersant additive, initiator and transfer agent are readily determinable by those skilled in the art.
  • the polymerization is carried out in a stirred reactor.
  • the optional fluoro comonomer it is advantageously chosen from compounds containing a vinyl group capable of being opened by the action of free radicals to polymerize and which contain, directly attached to this vinyl group, at least one fluorine atom. a fluoroalkyl group or a fluoroalkoxy group.
  • the proportion of VDF is at least 60% by weight for 40% of comonomer and preferably at least 85% by weight for 15% of comonomer.
  • the comonomer is advantageously chosen from HFP, CTFE, TFE and TRFE.
  • ZC n F 2n COOM in which Z is an atom of fluorine or chlorine, n is an integer of 6 to 13 and M is hydrogen or metal alkali or an ammonium group or an ammonium group having at least one lower alkyl substituent.
  • the total amount of surfactant introduced, at the start or during polymerization, may be between 0 and 5000 ppm of the PVDF manufactured (substantially equal to the total charge of fluorinated monomers used).
  • ammonium perfluorooctanoate and ammonium perfluorononanoate or mixtures thereof that is to say the product of formula ZC n F 2n COOM in which Z is F, M ammonium and average n is between 8 and 9.
  • the proportion of surfactant in the PVDF is determined by NMR analysis.
  • a paraffin is also added.
  • the paraffin used has a melting point ranging from 40 to 70 ° C. and represents from 0.005 to 0.05% by weight relative to the total weight of the fluorinated monomers.
  • the initiator and therefore the persulfate it is advantageously an alkaline persulfate and preferably a potassium or ammonium persulfate.
  • the initiator (or free radical initiator) used represents from 50 to 600 ppm and preferably from 100 to 400 ppm by weight relative to the total weight of the fluorinated monomer or monomers used.
  • NMR analysis revealed chain ends: -CF 2 -CH 2 -O-SO 3 ⁇
  • the polymer according to the invention has a chain end ratio as mentioned above of between 0.01 and 0.08 per 1000 VDF units.
  • transfer agent any product that limits the molecular weight of the polymer while propagating the polymerization reaction.
  • the transfer agents described in the prior art of the PVDF preparation are suitable. It most often has a hydrogen bond sensitive to a radical attack. By way of example, mention may be made of acetone, isopropanol, methyl acetate, ethyl acetate, diethyl ether, methyl tert-butyl ether, n-butyl acetate, diethyl malonate and the like. diethyl carbonate and various chlorofluorocarbon compounds.
  • the amount of transfer agent depends essentially on its nature and the average molar mass desired for the polymer fraction obtained in its presence, which conditions the average viscosity of the final product.
  • the transfer agent used represents from 0.05 to 5% by weight relative to the PVDF manufactured.
  • ethyl acetate is used.
  • the chain termination phenomenon generates perfectly identifiable terminations - CH 2 -CF 2 H and -CF 2 -CH 3 .
  • the radical resulting from the transfer reaction reinitiates new chains in greater proportions than the radicals generated by the decomposition of persulfate, which is why the ends: -CF 2 -CH 2 -O-SO 3 ⁇ represent only 0.3 to 1% of all detectable chain ends.
  • sodium acetate use is advantageously made of CH 3 -COONa 3H 2 O acetate trihydrate.
  • the proportion expressed as trihydrate is advantageously between 50 and 600 ppm relative to the PVDF manufactured.
  • the sodium brought by sodium acetate is measurable by X-ray fluorescence. It is expressed in Table 2 in weight ppm sodium relative to PVDF.
  • the proportion by weight relative to the PVDF manufactured can be between 0 and 300 ppm.
  • the alkyl groups R of this sulfonate are linear or branched and have from 1 to 11 carbon atoms. Ethyl, methyl, isopropyl and n-propyl are preferred.
  • the proportion of alkyl sulphonate in PVDF is determined by NMR analysis.
  • Thermal stability is also evaluated by plate molding.
  • the powder resulting from the drying of the latex is granulated in a coaxial twin-screw extruder CLEXTRAL® BC 21 at a temperature of 230 ° C. and a rotational speed of 120 rpm.
  • a ring die makes it possible to make pellets of 4 mm.
  • Using these granules plates 65 mm in diameter and 3 mm thick are pressed at 230 ° C for 9 min and 120 min at a pressure of 20 bar.
  • the color of the plates is measured using a Minolta® CR 200 colorimeter using the ASTM D 1925 standard for calculating the yellow index.
  • the latex is coagulated and washed before being atomized, which rids it of all water-soluble polymerization residues. Coagulation and washing are carried out according to the teaching of US Pat. No. 4128517.
  • the latex is diluted so as to have a solid content of 12%, and then introduced into a coagulator. 12 liters at a rate of 18l / h. Air is simultaneously introduced with a flow rate of 15 l / h.
  • the latex is coagulated by the shear produced by the turbine (blade tip speed 12 m / s) and converted into cream of lower density than that of water. This cream is introduced into a 14-liter washing column fed at the top by a flow rate of 140 l / h.
  • the coagulated and washed latex slurry exiting the washing column is introduced into an intermediate container from which it is sent into a 1 m3 atomizer.
  • the air temperature at the inlet of the atomizer is 140 ° C and 85 ° C at the outlet.
  • the powder obtained is then granulated using a CLEXTRAL® BC 21 extruder at 230 ° C., 120 rpm.
  • the latex is the same as in Comparative Example 1 and is subjected to a washing coagulation operation. The only difference is that after addition of coagulation and washing, an aqueous solution containing 15 g per liter of sodium acetate trihydrate and 5 g per liter of potassium ethylsulfonate is continuously added to the supply duct of the atomizer.
  • the feed rate of this solution is proportional to the PVDF feed rate so as to respect a ratio of sodium acetate trihydrate to PVDF of 0.00025.
  • the latex is the same as in Comparative Example 1.
  • the latex is first coagulated. It is diluted to have a solid content of 12%, and then introduced into a 12-liter coagulator at a rate of 18 l / h. Air is simultaneously introduced with a flow rate of 15 l / h.
  • the latex is coagulated by the shear produced by the turbine (blade tip speed 12 m / s) and converted into cream of lower density than that of water.
  • the coagulated dispersion is then diluted so as to reduce the level of solid to 6%.
  • the coagulated latex slurry concentrates up to 20% solids by gravity above an aqueous phase which is then removed by withdrawal. This way of operating is not effective enough to reduce the level of residual emulsifier to less than 300 ppm.
  • aqueous solution containing 15 g per liter of sodium acetate trihydrate and 5 g per liter of potassium ethyl sulfonate is added to the dispersion thus obtained.
  • the amount of solution added is 0.017 liter per kilogram of dry PVDF.
  • the dispersion thus additive is dried in a ventilated oven at 80 ° C. for 12 hours.
  • Table 1 example water (kg) Total VDF (kg) surfactant (g) pressure (bars) persulfate (g) sodium acetate (g) ethyl of K (g) PVDF (kg) dry extract poly time.

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Abstract

Production of polyvinylidene fluoride homo- or copolymers by persulfate-initiated radical polymerization in an aqueous dispersion comprises washing the product dispersion (optionally after coagulating it) to remove surfactant, adding sodium acetate and optionally a potassium alkylsulfonate, and drying the dispersion to obtain a powder containing less than 300 ppm surfactant. Production of polyvinylidene fluoride homo- or copolymers by radical polymerization of vinylidene fluoride and optionally a comonomer in an aqueous dispersion in the presence of a chain transfer agent, a persulfate initiator, optionally a surfactant and optionally a paraffin comprises washing the product dispersion (optionally after coagulating it) to remove surfactant, adding sodium acetate and optionally a potassium alkylsulfonate, and drying the dispersion to obtain a powder containing less than 300 ppm surfactant. An independent claim is also included for a polyvinylidene fluoride homo- or copolymer that contains sodium acetate, optionally contains a potassium alkylsulfonate, has a surfactant content below 300 ppm, has terminal CF2-CH2-OSO3-> groups and is produced using a persulfate initiator.

Description

Domaine de l'inventionField of the invention

Les polymères à base de fluorure de vinylidène CF2=CH2 (VDF) tels que par exemple le PVDF (polyfluorure de vinylidène) sont connus pour offrir d'excellentes propriétés de stabilité mécanique, une très grande inertie chimique, ainsi qu'une bonne résistance au vieillissement. Ces qualités sont exploitées pour des domaines d'application variés. On citera par exemple, la fabrication de pièces extrudées ou injectées pour l'industrie du génie chimique ou la microélectronique, l'utilisation sous forme de gaine d'étanchéité pour le transport des gaz ou des hydrocarbures, l'obtention de films ou de revêtements permettant la protection dans le domaine architectural, et la réalisation d'éléments protecteurs pour des usages électrotechniques.The polymers based on vinylidene fluoride CF 2 = CH 2 (VDF) such as for example PVDF (polyvinylidene fluoride) are known to offer excellent properties of mechanical stability, a very high chemical inertness, as well as a good resistance to aging. These qualities are exploited for various fields of application. For example, the manufacture of extruded or injected parts for the chemical engineering industry or microelectronics, the use in the form of a sealing sheath for the transport of gases or hydrocarbons, the production of films or coatings. allowing protection in the architectural field, and the production of protective elements for electrotechnical purposes.

La présente invention concerne un procédé de fabrication de PVDF homopolymère ou copolymère, plus précisément un procédé par polymérisation radicalaire du fluorure de vinylidène (VDF), et éventuellement d'un comonomère, en dispersion aqueuse en utilisant un persulfate comme initiateur (aussi appelé amorceur). On effectue la polymérisation éventuellement en présence d'un additif tensioactif encore appelé émulsifiant ou surfactant. On effectue un lavage de la dispersion de PVDF obtenue à l'issue de la polymérisation puis on ajoute de l'acétate de sodium et éventuellement un alkylsulfonate de potassium. Le PVDF obtenu doit contenir le moins possible de cet émulsifiant et en général de l'ordre de 300 ppm au plus.The present invention relates to a process for manufacturing PVDF homopolymer or copolymer, more specifically a process by radical polymerization of vinylidene fluoride (VDF), and optionally a comonomer, in aqueous dispersion using a persulfate as initiator (also called initiator) . The polymerization is carried out optionally in the presence of a surfactant additive also called emulsifier or surfactant. The PVDF dispersion obtained after the polymerization is washed, then sodium acetate and optionally potassium alkylsulphonate are added. The PVDF obtained must contain as little as possible of this emulsifier and in general of the order of 300 ppm at most.

L'art antérieur et le problème techniqueThe prior art and the technical problem

Le brevet US 4025709 décrit la polymérisation du VDF en présence de persulfate de potassium comme initiateur, d'acétate de sodium et d'un additif dispersant qui peut être un perfluorooctanoate de sodium (ex 1-3) ou un sulfonate de formule Rf-C2H4-SO3M dans laquelle M désigne un métal alcalin ou l'ammonium. La proportion d'additif dispersant par rapport au PVDF formé est comprise entre 550 et 2200 ppm. Le PVDF est obtenu sous forme d'un latex qu'on sèche à l'étuve ou qu'on sépare par centrifugation pour obtenir le PVDF. Il n'y a pas de lavage du latex, le PVDF contient donc entre 550 et 2200 ppm d'additif dispersant. Avec ce mode de séchage l'additif tensioactif n'est pas éliminé ou est très partiellement éliminé contrairement à l'invention revendiquée. US Pat . No. 4,025,709 describes the polymerization of VDF in the presence of potassium persulfate as initiator, of sodium acetate and of a dispersing additive which may be a sodium perfluorooctanoate (ex 1-3) or a sulfonate of formula Rf-C 2 H 4 -SO 3 M wherein M denotes an alkali metal or ammonium. The proportion of dispersing additive with respect to the PVDF formed is between 550 and 2200 ppm. The PVDF is obtained in the form of a latex which is dried in an oven or separated by centrifugation to obtain PVDF. There is no washing of the latex, the PVDF thus contains between 550 and 2200 ppm of dispersant additive. With this drying mode, the surfactant additive is not eliminated or is very partially eliminated contrary to the claimed invention.

Le brevet EP 169328 (US 4569978) décrit la polymérisation du VDF en présence de Diisopropyl peroxydicarbonate (IPP) comme initiateur et il n'y a pas d'acétate de sodium. Le brevet EP 816397 décrit un procédé similaire au précédent sauf que l'initiateur est du peroxyde de ditertiobutyle. EP 169328 (US 4569978) describes the polymerization of VDF in the presence of Diisopropyl peroxydicarbonate (IPP) as initiator and there is no sodium acetate. EP 816397 describes a process similar to the previous except that the initiator is di-tert-butyl peroxide.

Le brevet EP 387938 décrit la polymérisation du VDF en présence de persulfate d'ammonium comme initiateur, d'acétate d'éthyle comme agent de transfert de chaîne mais sans acétate de sodium ni additif dispersant. EP 387938 describes the polymerization of VDF in the presence of ammonium persulfate as initiator, ethyl acetate as a chain transfer agent but without sodium acetate or dispersant additive.

Le brevet US 5955556 décrit la polymérisation du VDF en présence d'un couple oxydant-réducteur mais sans additif dispersant ni acétate de sodium. L'oxydant peut être un persulfate. US Pat . No. 5,555,556 describes the polymerization of VDF in the presence of an oxidizing-reducing pair but without dispersing additive or sodium acetate. The oxidant may be a persulfate.

Le PVDF fabriqué selon les procédés décrits plus haut présente une stabilité thermique insuffisante pour des applications qui requièrent une transformation par extrusion, moulage par compression ou injection.The PVDF manufactured according to the methods described above has insufficient thermal stability for applications that require extrusion, compression molding or injection molding.

L'art antérieur a aussi décrit l'incorporation de sels dans le PVDF pour le stabiliser thermiquement. Le brevet FR 1298572 décrit du PVDF contenant des sels de baryum ou de strontium. Le brevet US 3728303 décrit la polymérisation du VDF en présence de persulfate d'ammonium comme initiateur mais sans additif dispersant. On ajoute ensuite dans le PVDF du chlorure ou du chlorate de sodium ou de potassium. Le brevet EP 870792 décrit la polymérisation du VDF en présence de persulfate comme initiateur et d'un additif dispersant qui est du perfluorooctanoate d'ammonium. On ajoute du nitrate de potassium soit au cours de la polymérisation du VDF soit dans le PVDF avant son introduction dans une extrudeuse. La demande de brevet BE 9600257 (US 5929152) décrit l'amélioration de la stabilité du PVDF par l'addition d'un sel de bismuth. La demande FR 2804438 décrit un procédé de préparation d'un polymère fluoré en émulsion aqueuse en présence d'un surfactant fluoré. L'addition d'acétate de sodium n'est pas suggérée.The prior art has also described the incorporation of salts in PVDF to thermally stabilize it. Patent FR 1298572 describes PVDF containing salts of barium or strontium. US Pat . No. 3,728,303 describes the polymerization of VDF in the presence of ammonium persulfate as an initiator but without any dispersant additive. Sodium or potassium chloride or chlorate is then added to the PVDF. EP 870792 describes the polymerization of VDF in the presence of persulfate as initiator and a dispersant additive which is ammonium perfluorooctanoate. Potassium nitrate is added either during the polymerization of VDF or in PVDF before it is introduced into an extruder. Patent Application BE 9600257 (US 5929152) describes the improvement of the stability of PVDF by the addition of a bismuth salt. The application FR 2804438 describes a process for preparing a fluorinated polymer in aqueous emulsion in the presence of a fluorinated surfactant. The addition of sodium acetate is not suggested.

On a maintenant trouvé qu'en effectuant la polymérisation en dispersion aqueuse en utilisant un persulfate comme initiateur et qu'en ajoutant de l'acétate de sodium et éventuellement un alkylsulfonate de potassium on obtenait un PVDF très stable thermiquement à condition que la stabilité thermique ne soit pas dégradée par des résidus indésirables de tensioactif. On effectue la polymérisation éventuellement en présence d'un additif tensioactif pour augmenter la quantité de PVDF produite par batch de polymérisation mais dans ce cas le PVDF obtenu doit contenir un niveau d'additif tensioactif résiduel suffisamment faible pour ne pas affecter la stabilité thermique. La teneur en additif tensioactif doit être inférieure à 300 ppm en poids par rapport au PVDF pour éviter une détérioration de la stabilité thermique. Pour arriver à ce niveau faible de résidu tensioactif on a découvert qu'il suffisait d'effectuer une coagulation de la dispersion aqueuse de PVDF obtenue à l'issue de sa polymérisation suivie d'un lavage à l'eau. Puis on ajoute l'acétate de sodium et éventuellement un alkylsulfonate de potassium dans la dispersion de PVDF et on récupère par séchage le PVDF en poudre.It has now been found that by carrying out the polymerization in aqueous dispersion using a persulfate as initiator and adding sodium acetate and optionally potassium alkylsulfonate a thermally stable PVDF is obtained provided that the thermal stability does not occur. not degraded by unwanted residues of surfactant. The polymerization is carried out optionally in the presence of a surfactant additive to increase the amount of PVDF produced per batch of polymerization but in this case the PVDF obtained must contain a residual surfactant additive level sufficiently low not to affect the thermal stability. The content of the surfactant additive must be less than 300 ppm by weight relative to the PVDF to avoid a deterioration of the thermal stability. To reach this low level of surfactant residue it was found that it was sufficient to coagulate the aqueous dispersion of PVDF obtained after its polymerization followed by washing with water. Sodium acetate and optionally potassium alkylsulphonate are then added to the PVDF dispersion and the PVDF powder is recovered by drying.

Brève description de l'inventionBrief description of the invention

La présente invention concerne un procédé de fabrication de PVDF homopolymère ou copolymère par polymérisation radicalaire du fluorure de vinylidène (VDF), et éventuellement d'un comonomère, en dispersion aqueuse en présence d'un agent de transfert, d'un persulfate comme initiateur radicalaire, éventuellement d'un additif tensioactif, éventuellement d'une paraffine, dans lequel :

  • a) on obtient une dispersion aqueuse de PVDF,
  • b) on effectue un lavage de la dispersion de l'étape a), éventuellement après l'avoir coagulée, pour abaisser la proportion de tensioactif éventuel dans le PVDF en dessous de 300 ppm, cette proportion étant exprimée par rapport au PVDF seché,
  • c) on ajoute dans la dispersion lavée en b) de l'acétate de sodium et éventuellement un alkylsulfonate de potassium,
  • d) on sèche par tout moyen la dispersion de l'étape c) pour récupérer le PVDF en poudre contenant l'acétate de sodium et éventuellement un alkylsulfonate de potassium.
The present invention relates to a process for producing PVDF homopolymer or copolymer by radical polymerization of vinylidene fluoride (VDF), and optionally a comonomer, in aqueous dispersion in the presence of a transfer agent, a persulfate as radical initiator optionally, a surfactant additive, optionally a paraffin, in which:
  • a) an aqueous dispersion of PVDF is obtained,
  • b) washing the dispersion of step a), optionally after coagulation, to reduce the proportion of potential surfactant in the PVDF below 300 ppm, this proportion being expressed relative to the dried PVDF,
  • c) sodium bicarbonate and optionally potassium alkylsulfonate are added to the washed dispersion in b),
  • d) the dispersion of step c) is dried by any means to recover the PVDF powder containing sodium acetate and optionally a potassium alkylsulfonate.

On obtient ainsi un PVDF contenant de l'acétate de sodium, éventuellement un alkylsulfonate de potassium et contenant moins de 300 ppm d'additif tensioactif. Il contient aussi des extrémités de chaîne :

        ―CF2―CH2―O―SO3 ⊖

provenant de l'utilisation du persulfate comme initiateur. Ce PVDF est très stable thermiquement. La présente invention concerne aussi ce PVDF en tant que produit nouveau.A PVDF containing sodium acetate, optionally a potassium alkylsulfonate and containing less than 300 ppm of surfactant additive, is thus obtained. It also contains chain ends:

-CF 2 -CH 2 -O-SO 3 ⊖

from the use of persulfate as initiator. This PVDF is very thermally stable. The present invention also relates to this PVDF as a new product.

Selon la nature de l'additif tensioactif et ses proportions le procédé est dit "en émulsion", ou tous autres procédés dérivés de l'émulsion (microsuspension, miniémulsion...) réalisable avec du persulfate comme amorçeur, lesquels sont parfaitement connus par l'homme de l'art. Après la fin de la polymérisation on sépare le PVDF de l'eau et des restes éventuels des réactifs engagés.Depending on the nature of the surfactant additive and its proportions, the process is referred to as "emulsion", or any other process derived from the emulsion (microsuspension, miniemulsion, etc.) that can be carried out with persulfate as an initiator, which are well known in the art. skilled in the art. After the end of the polymerization, the PVDF is separated from the water and any remains of the reagents involved.

Dans le cas des procédés type émulsion, le polymère se présente sous la forme d'un latex composé de particules très fines, dont le diamètre moyen est généralement inférieur à 1 micron. Ce latex peut être coagulé et éventuellement concentré en éliminant une partie de l'eau par exemple par centrifugation. Certains additifs tensioactif éventuellement utilisés à la polymérisation peuvent entraîner une dégradation de la stabilité thermique s'ils restent présents dans le PVDF. Puis on peut sécher le latex et simultanément éliminer le tensioactif en le mettant au contact d'un gaz chaud dans un atomiseur et on recueille le PVDF en poudre. Cette technique est connue et utilisée dans les procédés de fabrication du PVDF.In the case of emulsion type processes, the polymer is in the form of a latex composed of very fine particles, the average diameter of which is generally less than 1 micron. This latex can be coagulated and optionally concentrated by removing a portion of the water for example by centrifugation. Some surfactant additives that may be used in the polymerization may cause degradation of the thermal stability if they remain present in the PVDF. Then the latex can be dried and simultaneously remove the surfactant by bringing it into contact with a hot gas in an atomizer and the PVDF powder is collected. This technique is known and used in PVDF manufacturing processes.

Il peut néanmoins être nécessaire de faire un lavage dans le cas de tensioactifs à faible tension de vapeur ou lorsque la récupération des résidus de tensioactif dans les effluents gazeux de l'atomiseur présente des difficultés. Les techniques de lavage sont connues en elles mêmes. Un latex peut être coagulé par ajout de sel et l'eau éliminée par centrifugation ou filtration. Cette opération peut être répétée après ajout d'eau pure. Dans une autre technique le latex est dilué puis introduit dans un coagulateur ou il est soumis à un cisaillement en présence d'air. Sous l'effet cumulé de ces deux actions, le latex se transforme en crème aérée d'une densité inférieure à celle de l'eau.It may however be necessary to wash in the case of surfactants with low vapor pressure or when the recovery of the surfactant residues in the off-gas of the atomizer presents difficulties. Washing techniques are known per se. A latex can be coagulated by adding salt and the water removed by centrifugation or filtration. This operation can be repeated after adding pure water. In another technique, the latex is diluted and then introduced into a coagulator or it is subjected to shearing in the presence of air. Under the cumulative effect of these two actions, the latex is transformed into aerated cream with a density lower than that of water.

Cette crème est éventuellement lavée à contre-courant avec de l'eau déionisée par exemple selon le procédé décrit dans les brevets US 4,128,517 et EP 0 460 284. Le lavage à l'eau permet de débarrasser le latex du tensioactif qui était nécessaire pour la polymérisation ou au moins de fortement réduire sa proportion par rapport au PVDF.This cream is optionally backwashed with deionized water, for example according to the process described in US Pat. No. 4,128,517. and EP 0 460 284. Washing with water makes it possible to rid the latex of the surfactant which was necessary for the polymerization or at least to greatly reduce its proportion relative to the PVDF.

On ajoute ensuite l'acétate de sodium et l'alkylsulfonate de potassium éventuel. La dispersion de PDVF lavée contenant l'acétate de sodium et l'alkylsulfonate de sodium peut être séchée par tout procédé de séchage. Le séchage par atomisation ou séchage dans un sécheur rotatif conviennent particulièrement.Sodium acetate and optional potassium alkylsulfonate are then added. The washed PDVF dispersion containing sodium acetate and sodium alkylsulfonate can be dried by any drying method. Spray drying or drying in a rotary dryer are particularly suitable.

Selon une forme avantageuse l'invention est un procédé discontinu ou semi-continu de fabrication de PVDF homopolymère ou copolymère dans lequel :

  • on charge le réacteur de polymérisation avec de l'eau, l'additif tensioactif éventuel et éventuellement une paraffine,
  • le réacteur est désaéré pour éliminer l'oxygène,
  • le réacteur est porté à la température choisie et on charge le VDF et le monomère éventuel jusqu'à atteindre la pression voulue,
  • l'agent de transfert est introduit dans le réacteur soit en totalité soit en partie au départ et en partie au cours de la polymérisation,
  • on ajoute le persulfate (l'initiateur) en totalité ou en partie pour démarrer la polymérisation et la baisse de pression qui en résulte est compensée par l'ajout de VDF et du comonomère éventuel,
  • le reste éventuel de l'initiateur est ajouté au cours de la polymérisation,
  • après introduction de la quantité prévue de VDF et de comonomère éventuel le réacteur est dégazé et on obtient une dispersion aqueuse de PVDF,
  • on effectue un lavage de la dispersion aqueuse de PVDF éventuellement après l'avoir coagulée, pour abaisser la proportion de tensioactif éventuel dans le PVDF en dessous de 300 ppm, cette proportion étant exprimée par rapport au PVDF seché,
  • on ajoute dans la dispersion lavée de l'acétate de sodium et éventuellement un alkylsulfonate de potassium,
  • on sèche par tout moyen la dispersion de l'étape précédente pour récupérer le PVDF en poudre contenant l'acétate de sodium et éventuellement un alkylsulfonate de potassium.
According to an advantageous form, the invention is a batch or semi-continuous process for producing PVDF homopolymer or copolymer in which:
  • the polymerization reactor is charged with water, the optional surfactant additive and optionally a paraffin,
  • the reactor is de-aerated to eliminate the oxygen,
  • the reactor is brought to the chosen temperature and the VDF and the optional monomer are loaded until the desired pressure is reached,
  • the transfer agent is introduced into the reactor either wholly or partly initially and partly during the polymerization,
  • the persulfate (the initiator) is added in whole or in part to start the polymerization and the resulting pressure drop is compensated by the addition of VDF and the optional comonomer,
  • the remainder of the initiator is added during the polymerization,
  • after introducing the expected amount of VDF and any comonomer the reactor is degassed and an aqueous dispersion of PVDF is obtained,
  • the aqueous dispersion of PVDF is washed optionally after having been coagulated, in order to lower the proportion of possible surfactant in the PVDF below 300 ppm, this proportion being expressed relative to the dried PVDF,
  • sodium acetate and optionally potassium alkylsulfonate are added to the washed dispersion,
  • the dispersion of the preceding step is dried by any means to recover the PVDF powder containing sodium acetate and optionally potassium alkylsulphonate.

La température choisie est la température suffisante pour polymériser le VDF et est de l'ordre de 45 à 130°C et avantageusement entre 70 et 90°C. La pression voulue est de l'ordre de 35 à 125 bars.The temperature chosen is the temperature sufficient to polymerize the VDF and is of the order of 45 to 130 ° C and advantageously between 70 and 90 ° C. The desired pressure is of the order of 35 to 125 bars.

Le volume d'eau dans lequel on réalise la dispersion des monomères, les quantités d'additif dispersant, d'initiateur et d'agent de transfert sont déterminables facilement par l'homme de métier. On effectue la polymérisation dans un réacteur agité.The volume of water in which the dispersion of the monomers is carried out, the amounts of dispersant additive, initiator and transfer agent are readily determinable by those skilled in the art. The polymerization is carried out in a stirred reactor.

Description détaillée de l'inventionDetailed description of the invention

S'agissant du comonomère fluoré éventuel il est avantageusement choisi parmi les composés contenant un groupe vinyle capable de s'ouvrir par l'action de radicaux libres pour se polymériser et qui contiennent, directement attaché à ce groupe vinyle, au moins un atome de fluor, un groupe fluoroalkyle ou un groupe fluoroalkoxy. A titre d'exemple de comonomère on peut citer le fluorure de vinyle; le trifluoroethylene (TRFE); le chlorotrifluoroethylene (CTFE); le 1,2-difluoroethylene; le tetrafluoroethylene (TFE); l'hexafluoropropylene (HFP); les perfluoro(alkyl vinyl) ethers tels que le perfluoro(methyl vinyl)ether (PMVE), le perfluoro(ethyl vinyl) ether (PEVE) et le perfluoro(propyl vinyl) ether (PPVE); le perfluoro(1,3 -dioxole); le perfluoro(2,2-dimethyl- 1,3 -dioxole) (PDD); le produit de formule CF2=CFOCF2CF(CF3)OCF2CF2X dans laquelle X est SO2F, CO2H, CH2OH, CH2OCN ou CH2OPO3H; le produit de formule CF2=CFOCF2CF2SO2F; le produit de formule F(CF2)nCH20CF=CF2 dans laquelle n est 1, 2, 3, 4 or 5; le produit de formule R1CH2OCF=CF2 dans laquelle R1 est l'hydrogene ou F(CF2)z et z vaut 1, 2, 3 ou 4; le produit de formule R3OCF=CH2 dans laquelle R3 est F(CF2)z- et z est 1, 2, 3 or 4; le perfluorobutyl ethylene (PFBE); le 3,3,3-trifluoropropene et le 2-trifluoromethyl-3 ,3 ,3 -trifluoro- 1 -propene. On peut utiliser plusieurs comonomères. S'agissant du PVDF copolymère la proportion de VDF est d'au moins 60% en poids pour 40% de comonomère et de préférence d'au moins 85% en poids pour 15% de comonomère. Le comonomère est avantageusement choisi parmi l'HFP, le CTFE, le TFE et le TRFE. As regards the optional fluoro comonomer, it is advantageously chosen from compounds containing a vinyl group capable of being opened by the action of free radicals to polymerize and which contain, directly attached to this vinyl group, at least one fluorine atom. a fluoroalkyl group or a fluoroalkoxy group. As an example of a comonomer, mention may be made of vinyl fluoride; trifluoroethylene (TRFE); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro (alkyl vinyl) ethers such as perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE) and perfluoro (propyl vinyl) ether (PPVE); perfluoro (1,3-dioxole); perfluoro (2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF 2 = CFOCF 2 CF (CF 3 ) OCF 2 CF 2 X in which X is SO 2 F, CO 2 H, CH 2 OH, CH 2 OCN or CH 2 OPO 3 H; the product of formula CF 2 = CFOCF 2 CF 2 SO 2 F; the product of formula F (CF 2 ) n CH 2 0CF = CF 2 in which n is 1, 2, 3, 4 or 5; the product of formula R 1 CH 2 OCF = CF 2 in which R 1 is hydrogen or F (CF 2 ) z and z is 1, 2, 3 or 4; the product of formula R 3 OCF = CH 2 in which R 3 is F (CF 2 ) z- and z is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene. We can use several comonomers. With regard to the PVDF copolymer, the proportion of VDF is at least 60% by weight for 40% of comonomer and preferably at least 85% by weight for 15% of comonomer. The comonomer is advantageously chosen from HFP, CTFE, TFE and TRFE.

S'agissant du tensioactif, dans les procédés en émulsion on utilise avantageusement un tensioactif ionique dérivé d'un acide ou une d'une base organique. Les brevets US 4025709, US 4569978, US 4360652, EP 626396 et EP 0655468 décrivent les procédés de synthèse du PVDF par mise en émulsion aqueuse du VF2 et sa polymérisation, on y trouve de nombreuses formules de tensioactifs. Regarding the surfactant in the emulsion processes are advantageously used an ionic derivative of an acid or of an organic base. The patents US 4025709, US Pat. No. 4,566,478, US Pat. No. 4,360,662, EP 626,396 and EP 0655468 describe the processes for synthesizing PVDF by aqueous emulsification of the VF 2 and its polymerization, there are numerous surfactant formulas.

A titre d'exemple on peut citer ceux de formule générale : ZCnF2nCOOM dans laquelle Z est un atome de fluor ou de chlore, n est un nombre entier valant 6 à 13 et M est un atome d'hydrogène ou de métal alcalin ou un groupe ammonium ou un groupe ammonium comportant au moins un substituant alkyle inférieur.For example there may be mentioned those of general formula: ZC n F 2n COOM in which Z is an atom of fluorine or chlorine, n is an integer of 6 to 13 and M is hydrogen or metal alkali or an ammonium group or an ammonium group having at least one lower alkyl substituent.

On peut encore citer les perfluoroalkanoates de lithium de formule F3C(CF2)n-2CO2Li où n = 7, 8, 9 et 10.Mention may also be made of lithium perfluoroalkanoates of formula F 3 C (CF 2 ) n-2 CO 2 Li where n = 7, 8, 9 and 10.

La quantité totale de tensioactif introduite, au départ ou en cours de polymérisation, peut être comprise entre 0 et 5000 ppm du PVDF fabriqué (sensiblement égal à la charge totale de monomères fluorés mis en oeuvre).The total amount of surfactant introduced, at the start or during polymerization, may be between 0 and 5000 ppm of the PVDF manufactured (substantially equal to the total charge of fluorinated monomers used).

Avantageusement on utilise le perfluorooctanoate d'ammonium et le perfluorononanoate d'ammonium ou leur mélanges, c'est à dire le produit de formule ZCnF2nCOOM dans laquelle Z est F, M l'ammonium et n moyen est compris entre 8 et 9.Advantageously, ammonium perfluorooctanoate and ammonium perfluorononanoate or mixtures thereof, that is to say the product of formula ZC n F 2n COOM in which Z is F, M ammonium and average n is between 8 and 9.

La proportion de tensioactif dans le PVDF est déterminée par analyse RMN.The proportion of surfactant in the PVDF is determined by NMR analysis.

Avantageusement on ajoute aussi, en plus du tensioactif, une paraffine. La paraffine mise en oeuvre a un point de fusion allant de 40 à 70°C et représente de 0,005 à 0.05 % en poids par rapport au poids total des monomères fluorés. Advantageously, in addition to the surfactant, a paraffin is also added. The paraffin used has a melting point ranging from 40 to 70 ° C. and represents from 0.005 to 0.05% by weight relative to the total weight of the fluorinated monomers.

S'agissant de l'amorceur et donc le persulfate , c'est avantageusement un persulfate alcalin et de préférence un persulfate de potassium ou d'ammonium. As regards the initiator and therefore the persulfate, it is advantageously an alkaline persulfate and preferably a potassium or ammonium persulfate.

Avantageusement l'amorceur (ou initiateur radicalaire) mis en oeuvre représente de 50 à 600 ppm et de préférence 100 à 400 ppm en poids par rapport au poids total du ou des monomères fluorés mis en oeuvre.
L'analyse RMN a mis en évidence des extrémités de chaîne :

        ―CF2―CH2―O―SO3 ⊖

Advantageously, the initiator (or free radical initiator) used represents from 50 to 600 ppm and preferably from 100 to 400 ppm by weight relative to the total weight of the fluorinated monomer or monomers used.
NMR analysis revealed chain ends:

-CF 2 -CH 2 -O-SO 3 ⊖

Il est possible de quantifier le nombre de ces extrémités de chaîne par le rapport de leur nombre ramené à 1000 motifs de VDF. Ce taux dépend des masses moléculaires et de la quantité de persulfate utilisé. Le polymère selon l'invention a un taux d'extrémités de chaînes telles que citées plus haut compris entre 0.01 et 0,08 pour 1000 motifs VDF.It is possible to quantify the number of these chain ends by the ratio of their number down to 1000 VDF patterns. This rate depends on the molecular weights and the amount of persulfate used. The polymer according to the invention has a chain end ratio as mentioned above of between 0.01 and 0.08 per 1000 VDF units.

S'agissant de l'agent de transfert, on désigne ainsi tout produit qui permet de limiter la masse molaire du polymère tout en propageant la réaction de polymérisation. Les agents de transfert décrits dans l'art antérieur de la préparation du PVDF conviennent. Il présente le plus souvent une liaison hydrogène sensible à une attaque radicalaire. A titre d'exemple on peut citer l'acétone, l'isopropanol, l'acétate de méthyle, l'acétate d'éthyle, le diethylether, le méthyltertiobutyle ether, l'acétate de n-butyle, le malonate de diéthyle et le carbonate de diéthyle et différents composés chlorofluorocarbonés. La quantité d'agent de transfert dépend essentiellement de sa nature et de la masse molaire moyenne désirée pour la fraction de polymère obtenue en sa présence, laquelle conditionne la viscosité moyenne du produit final. De préférence, l'agent de transfert mis en oeuvre représente de 0,05 à 5 % en poids par rapport au PVDF fabriqué. Avantageusement on utilise l'acétate d'éthyle. With regard to the transfer agent, is meant any product that limits the molecular weight of the polymer while propagating the polymerization reaction. The transfer agents described in the prior art of the PVDF preparation are suitable. It most often has a hydrogen bond sensitive to a radical attack. By way of example, mention may be made of acetone, isopropanol, methyl acetate, ethyl acetate, diethyl ether, methyl tert-butyl ether, n-butyl acetate, diethyl malonate and the like. diethyl carbonate and various chlorofluorocarbon compounds. The amount of transfer agent depends essentially on its nature and the average molar mass desired for the polymer fraction obtained in its presence, which conditions the average viscosity of the final product. Preferably, the transfer agent used represents from 0.05 to 5% by weight relative to the PVDF manufactured. Advantageously, ethyl acetate is used.

Le phénomène de terminaison de chaînes génère des terminaisons - CH2-CF2H et -CF2-CH3 parfaitement identifiables. Le radical issu de la réaction de transfert réinitie de nouvelles chaînes dans des proportions plus importantes que les radicaux générés par la décomposition du persulfate c'est la raison pour laquelle les extrémités :

        ―CF2―CH2―O―SO3 ⊖

ne représentent que 0,3 à 1% de l'ensemble des extrémités de chaîne détectables.The chain termination phenomenon generates perfectly identifiable terminations - CH 2 -CF 2 H and -CF 2 -CH 3 . The radical resulting from the transfer reaction reinitiates new chains in greater proportions than the radicals generated by the decomposition of persulfate, which is why the ends:

-CF 2 -CH 2 -O-SO 3 ⊖

represent only 0.3 to 1% of all detectable chain ends.

S'agissant de l'acétate de sodium on utilise avantageusement l'acétate trihydrate CH3-COONa, 3H2O. La proportion exprimée en trihydrate est avantageusement comprise entre 50 et 600 ppm par rapport au PVDF fabriqué. Le sodium amené par l'acétate de sodium est mesurable par fluorescence X. Il est exprimé dans le tableau 2 en ppm pondéral de sodium par rapport au PVDF. With regard to the sodium acetate, use is advantageously made of CH 3 -COONa 3H 2 O acetate trihydrate. The proportion expressed as trihydrate is advantageously between 50 and 600 ppm relative to the PVDF manufactured. The sodium brought by sodium acetate is measurable by X-ray fluorescence. It is expressed in Table 2 in weight ppm sodium relative to PVDF.

S'agissant de l'alkyle sulfonate de potassium (R-SO3K) la proportion en poids par rapport au PVDF fabriqué peut être comprise entre 0 et 300 ppm. Les groupes alkyles R de ce sulfonate sont linéaires ou ramifiés et ont de 1 à 11 atomes de carbone. On préfère l'éthyle, le méthyle, l'isopropyle et le n-propyle. La proportion d'alkyle sulfonate dans le PVDF est déterminée par analyse RMN. As regards the potassium alkyl sulphonate (R-SO 3 K) the proportion by weight relative to the PVDF manufactured can be between 0 and 300 ppm. The alkyl groups R of this sulfonate are linear or branched and have from 1 to 11 carbon atoms. Ethyl, methyl, isopropyl and n-propyl are preferred. The proportion of alkyl sulphonate in PVDF is determined by NMR analysis.

Évaluation de la stabilité thermique : A partir de 40g de poudre (de PVDF) on forme par moulage par compression sous 30 bars et à 205°C pendant 6 minutes une plaque de 260x20x4mm qui est soumise à une trempe à l'eau à 20°C. La plaque est ensuite réchauffée dans un four Metrastat® PSD 260 à 265°C pendant 1h. Après ce traitement thermique la plaque peut être plus ou moins colorée. La couleur est déterminée par une mesure de jaunissement. La plaque est mise sur une céramique blanche calibrée et l'indice de jaunissement est mesuré à l'aide d'un colorimètre de marque Minolta® CR 200 en utilisant la norme ASTM D 1925 pour le calcul de l'indice de jaune. Evaluation of the thermal stability: From 40 g of powder (PVDF) is formed by compression molding at 30 bar and at 205 ° C for 6 minutes a 260x20x4mm plate which is subjected to a quenching with water at 20 ° vs. The plate is then reheated in a Metrastat® PSD 260 oven at 265 ° C for 1 hour. After this heat treatment the plate can be more or less colored. The color is determined by a measure of yellowing. The plate is placed on a calibrated white ceramic and the index Yellowness was measured using a Minolta® CR 200 colorimeter using ASTM D 1925 for calculating the yellow index.

On évalue aussi la stabilité thermique par un moulage de plaque. La poudre issue du séchage du latex est granulée dans une extrudeuse CLEXTRAL® BC 21 double vis corotative à une température de 230°C et une vitesse de rotation de 120 tours par minute. Une filière à jonc permet de faire des granulés de 4 mm. A l'aide de ces granulés des plaques de 65 mm de diamètre et 3 mm d'épaisseur sont pressées à 230°C pendant 9 min et 120 min à une pression de 20 bars. La coloration des plaques est mesurée à l'aide d'un colorimètre de marque Minolta® CR 200 en utilisant la norme ASTM D 1925 pour le calcul de l'indice de jaune.Thermal stability is also evaluated by plate molding. The powder resulting from the drying of the latex is granulated in a coaxial twin-screw extruder CLEXTRAL® BC 21 at a temperature of 230 ° C. and a rotational speed of 120 rpm. A ring die makes it possible to make pellets of 4 mm. Using these granules plates 65 mm in diameter and 3 mm thick are pressed at 230 ° C for 9 min and 120 min at a pressure of 20 bar. The color of the plates is measured using a Minolta® CR 200 colorimeter using the ASTM D 1925 standard for calculating the yellow index.

ExemplesExamples Exemple comparatif 1Comparative Example 1

Dans un réacteur de 30 litres sont introduits à température ambiante :

  • 17 litres d'eau déionisée,
  • 2 g de paraffine de point de fusion égal à 60°C,
  • 52.8 g d'une solution à 15% de perfluorooctanoate d'ammonium.
    Après fermeture et désaération le réacteur est mis sous agitation et chauffé à 83°C. Après introduction de 88 g d'acétate d'éthyle le réacteur est pressurisé à 45 bars avec du VDF. Après injection de 300 g d'une solution de persulfate de potassium à 0,5% en poids, la polymérisation démarre et la pression est maintenue à 45 bars par du VDF. Après introduction de 1500 g de VDF on rajoute 100 g d'une solution de persulfate de potassium à 0,5% en poids. Après introduction de 8500 g de VDF au total (temps= 4h30) on laisse baisser la pression jusqu'à 15 bars et on dégaze le monomère résiduaire. Le latex est filtré. Le poids de latex obtenu est de 26,4 kg. Le taux de matières sèches (ou extrait sec) est de 30%.
In a 30 liter reactor are introduced at room temperature:
  • 17 liters of deionized water,
  • 2 g of paraffin with a melting point of 60 ° C.
  • 52.8 g of a 15% solution of ammonium perfluorooctanoate.
    After closing and deaeration the reactor is stirred and heated to 83 ° C. After introduction of 88 g of ethyl acetate the reactor is pressurized to 45 bar with VDF. After injection of 300 g of 0.5% by weight potassium persulfate solution, the polymerization starts and the pressure is maintained at 45 bar by VDF. After introduction of 1500 g of VDF, 100 g of a solution of potassium persulfate at 0.5% by weight are added. After introduction of 8500 g of VDF in total (time = 4:30), the pressure is allowed to drop to 15 bar and the residual monomer is degassed. The latex is filtered. The latex weight obtained is 26.4 kg. The rate of dry matter (or dry extract) is 30%.

Le latex est coagulé et lavé avant d'être atomisé,ce qui le débarrasse de tous les résidus de polymérisation hydrosolubles. La coagulation et le lavage sont effectués selon l'enseignement du brevet US 4128517. Le latex est dilué de manière à avoir un taux de solide de 12%, puis introduit dans un coagulateur de 12 litres à un débit de 18l/h. On introduit simultanément de l'air avec un débit de 15 l/h. Le latex est coagulé par le cisaillement produit par la turbine (vitesse de bout de pale 12 m/s) et transformé en crème de densité inférieure à celle de l'eau. Cette crème est introduite dans une colonne de lavage de 14 litres alimentée en tête par un débit de 140 l/h. La bouillie de latex coagulé et lavé sortant de la colonne de lavage est introduite dans un récipient intermédiaire à partir duquel elle est envoyée dans un atomiseur de 1 m3. La température de l'air à l'entrée de l'atomiseur est de 140°C et de 85°C à la sortie. La poudre obtenue est ensuite granulée à l'aide d'une extrudeuse CLEXTRAL® BC 21 à 230°C, 120 tr/min.The latex is coagulated and washed before being atomized, which rids it of all water-soluble polymerization residues. Coagulation and washing are carried out according to the teaching of US Pat. No. 4128517. The latex is diluted so as to have a solid content of 12%, and then introduced into a coagulator. 12 liters at a rate of 18l / h. Air is simultaneously introduced with a flow rate of 15 l / h. The latex is coagulated by the shear produced by the turbine (blade tip speed 12 m / s) and converted into cream of lower density than that of water. This cream is introduced into a 14-liter washing column fed at the top by a flow rate of 140 l / h. The coagulated and washed latex slurry exiting the washing column is introduced into an intermediate container from which it is sent into a 1 m3 atomizer. The air temperature at the inlet of the atomizer is 140 ° C and 85 ° C at the outlet. The powder obtained is then granulated using a CLEXTRAL® BC 21 extruder at 230 ° C., 120 rpm.

Exemple 1Example 1

Le latex est le même que dans l'exemple comparatif 1 et est soumis à une opération de coagulation lavage . La seule différence est que l'on rajoute après coagulation et lavage une solution aqueuse contenant 15g par litre d'acétate de sodium trihydrate et 5g par litre d'ethyle sulfonate de potassium en continu dans le conduit d'alimentation de l'atomiseur. Le débit d'alimentation de cette solution est proportionnel au débit d'alimentation en PVDF de manière à respecter un rapport acétate de sodium trihydrate sur PVDF de 0.00025The latex is the same as in Comparative Example 1 and is subjected to a washing coagulation operation. The only difference is that after addition of coagulation and washing, an aqueous solution containing 15 g per liter of sodium acetate trihydrate and 5 g per liter of potassium ethylsulfonate is continuously added to the supply duct of the atomizer. The feed rate of this solution is proportional to the PVDF feed rate so as to respect a ratio of sodium acetate trihydrate to PVDF of 0.00025.

Exemple comparatif 2Comparative Example 2

Le latex est le même que dans l'exemple comparatif 1.The latex is the same as in Comparative Example 1.

Le latex est d'abord coagulé. Il est dilué de manière à avoir un taux de solide de 12%, puis introduit dans un coagulateur de 12 litres à un débit de 18l/h. On introduit simultanément de l'air avec un débit de 15 l/h. Le latex est coagulé par le cisaillement produit par la turbine (vitesse de bout de pale 12 m/s) et transformé en crème de densité inférieure à celle de l'eau. La dispersion coagulée est ensuite diluée de manière à ramener le taux de solide à 6%. La bouillie de latex coagulé, se concentre jusqu'à 20% de taux de solide par gravité au dessus d'une phase aqueuse qui est ensuite éliminée par soutirage. Cette façon d'opérer n'est pas assez efficace pour diminuer le taux d'émulsifiant résiduaire à moins de 300 ppm. On ajoute à la dispersion ainsi obtenue une solution aqueuse contenant 15g par litre d'acétate de sodium trihydrate et 5g par litre d'éthyle sulfonate de potassium. La quantité de solution ajoutée est de 0.017 litre par kilogramme de PVDF sec. La dispersion ainsi additivée est séchée dans une étuve ventilée à 80°C pendant 12 heures.The latex is first coagulated. It is diluted to have a solid content of 12%, and then introduced into a 12-liter coagulator at a rate of 18 l / h. Air is simultaneously introduced with a flow rate of 15 l / h. The latex is coagulated by the shear produced by the turbine (blade tip speed 12 m / s) and converted into cream of lower density than that of water. The coagulated dispersion is then diluted so as to reduce the level of solid to 6%. The coagulated latex slurry concentrates up to 20% solids by gravity above an aqueous phase which is then removed by withdrawal. This way of operating is not effective enough to reduce the level of residual emulsifier to less than 300 ppm. An aqueous solution containing 15 g per liter of sodium acetate trihydrate and 5 g per liter of potassium ethyl sulfonate is added to the dispersion thus obtained. The amount of solution added is 0.017 liter per kilogram of dry PVDF. The dispersion thus additive is dried in a ventilated oven at 80 ° C. for 12 hours.

Exemple 2Example 2

Dans un réacteur de 30 litres sont introduits à température ambiante :

  • 17 litres d'eau déionisée,
  • 2 g de paraffine de point de fusion égal à 60°C,
  • 52.8 g d'une solution à 15% de perfluorooctanoate d'ammonium.
    Après fermeture et désaération le réacteur est mis sous agitation et chauffé à 83°C. Après introduction de 22.5 g d'acétate d'éthyle le réacteur est pressurisé à 45 bars avec du VDF. Après injection de 300 g d'une solution de persulfate de potassium à 0,5% en poids, la polymérisation démarre et la pression est maintenue à 45 bars par du VDF. On introduit en cours de polymérisation 125g d'acétate d'éthyle et 220 g d'une solution à 0.5% de persulfate de potassium . Après introduction de 8500 g de VDF au total (temps= 4h20) on laisse baisser la pression jusqu'à 15 bars et on dégaze le monomère résiduaire. Le latex est filtré. Le poids de latex obtenu est de 26 kg. Le taux de matières sèches (ou extrait sec) est de 29%.
In a 30 liter reactor are introduced at room temperature:
  • 17 liters of deionized water,
  • 2 g of paraffin with a melting point of 60 ° C.
  • 52.8 g of a 15% solution of ammonium perfluorooctanoate.
    After closing and deaeration the reactor is stirred and heated to 83 ° C. After introduction of 22.5 g of ethyl acetate the reactor is pressurized to 45 bar with VDF. After injection of 300 g of 0.5% by weight potassium persulfate solution, the polymerization starts and the pressure is maintained at 45 bar by VDF. 125 g of ethyl acetate and 220 g of a 0.5% solution of potassium persulfate are introduced during polymerization. After introduction of 8500 g of VDF in total (time = 4.20 hours), the pressure is allowed to drop to 15 bars and the residual monomer is degassed. The latex is filtered. The latex weight obtained is 26 kg. The rate of dry matter (or dry extract) is 29%.

On rajoute après coagulation et lavage effectués comme dans l'exemple comparatif 1 une solution aqueuse contenant 15g par litre d'acétate de sodium trihydrate et 7.5g par litre d'ethyle sulfonate de potassium en continu dans le conduit d'alimentation de l'atomiseur. Le débit d'alimentation de cette solution est proportionnel au débit d'alimentation en PVDF de manière à respecter un rapport acétate de sodium trihydrate sur PVDF de 0.00025
La bouillie de PVDF est atomisée dans les mêmes conditions que dans l'exemple comparatif 1.After coagulation and washing, as in Comparative Example 1, an aqueous solution containing 15 g per liter of sodium acetate trihydrate and 7.5 g per liter of potassium ethylsulphonate is continuously added in the supply duct of the atomizer. . The feed rate of this solution is proportional to the PVDF feed rate so as to respect a ratio of sodium acetate trihydrate to PVDF of 0.00025.
The PVDF slurry is atomized under the same conditions as in Comparative Example 1.

Les résultats sont sur les tableaux 1 et 2 ci après. Tableau 1 exemple eau (kg) VDF total (kg) tensioactif (g) pression (bars) persulfate (g) acétate de sodium (g) éthyle de K (g) PVDF (kg) extrait sec temps de poly. Comp 1 17 8500 7.9 45 2 0 0 7900 30% 4h30 1 17 8500 7.9 45 2 2 0.6 7900 30% 4h30 2 17 8500 7.9 45 2.1 2.1 1,30 7900 29% 4h20 Comp 2 17 8500 7.9 45 2 2 0.66 7900 30% 4h30 Tableau 2 exemple caractérisation analytique des granulés stabilité thermique YI extrémités O-SO3- pour 1000 VDF tensioactif résiduaire ppm/PVDF Na ppm/PVDF éthyle sulfonate ppm/PVDF Metrastat 1h 265°C moulage de plaque 2h à 230°C moulage de plaque 9 min à 230°C Comp 1 0.04 160 Non détecté 0 50 40 25 1 0.04 160 35 60 29 22 14 2 0.04 180 36 110 27 20 14 Comp 2 0.04 500 32 58 50 41 30 The results are in Tables 1 and 2 below. Table 1 example water (kg) Total VDF (kg) surfactant (g) pressure (bars) persulfate (g) sodium acetate (g) ethyl of K (g) PVDF (kg) dry extract poly time. Comp 1 17 8500 7.9 45 two 0 0 7900 30% 4:30 1 17 8500 7.9 45 two two 0.6 7900 30% 4:30 two 17 8500 7.9 45 2.1 2.1 1.30 7900 29% 4:20 Comp 2 17 8500 7.9 45 two two 0.66 7900 30% 4:30 example analytical characterization of granules thermal stability YI O-SO3 ends for 1000 VDF residual surfactant ppm / PVDF Na ppm / PVDF ethyl sulfonate ppm / PVDF Metrastat 1h 265 ° C plate molding 2h at 230 ° C plate molding 9 min at 230 ° C Comp 1 0.04 160 Not detected 0 50 40 25 1 0.04 160 35 60 29 22 14 two 0.04 180 36 110 27 20 14 Comp 2 0.04 500 32 58 50 41 30

Claims (6)

  1. Process for the manufacture of PVDF homopolymer or copolymer by radical polymerization of vinylidene fluoride (VDF), and optionally of a comonomer, in aqueous dispersion and in the presence of a transfer agent, of a persulphate as radical initiator, optionally of a surface-active additive and optionally of a paraffin wax, in which:
    a) an aqueous PVDF dispersion is obtained,
    b) the dispersion from stage a) is washed, optionally after having coagulated it, in order to lower the proportion of possible surfactant in the PVDF below 300 ppm, this proportion being expressed with respect to the dried PVDF,
    c) sodium acetate and optionally a potassium alkylsulphonate are added to the dispersion washed in b),
    d) the dispersion from stage c) is dried by any means in order to recover the PVDF as a powder comprising the sodium acetate and optionally a potassium alkylsulphonate.
  2. Process according to Claim 1, in which the surface-active additive is chosen from those of general formula: ZCnF2nCOOM
    in which Z is a fluorine or chlorine atom, n is an integer with a value from 6 to 13 and M is a hydrogen or alkali metal atom or an ammonium group or an ammonium group comprising at least one lower alkyl substituent.
  3. Process according to either one of the preceding claims, in which the proportion of sodium acetate is between 50 and 600 ppm with respect to the PVDF manufactured.
  4. Process according to any one of the preceding claims, in which the potassium alkylsulphonate is chosen from potassium ethylsulphonate, methylsulphonate, isopropylsulphonate and n-propylsulphonate.
  5. Process according to any one of the preceding claims, in which the proportion of potassium alkylsulphonate is between 0 and 300 ppm with respect to the PVDF manufactured.
  6. Batchwise or semi-continuous process according to one of Claims 1 to 5, in which:
    • the polymerization reactor is charged with water, the optional surface-active additive and optionally a paraffin wax,
    • the reactor is deaerated to remove the oxygen,
    • the reactor is brought to the chosen temperature and VDF and the optional monomer are charged until the desired pressure is reached,
    • the transfer agent is introduced into the reactor, either in its entirety or partly at the start of and partly during the polymerization,
    • the persulphate (the initiator) is added, in its entirety or in part, to start the polymerization and the fall in pressure which results therefrom is compensated for by the addition of VDF and of the optional comonomer,
    • the possible remaining initiator is added during the polymerization,
    • after introduction of the planned amount of VDF and of optional comonomer, the reactor is degassed and an aqueous PVDF dispersion is obtained,
    • the aqueous PVDF dispersion is washed, optionally after having coagulated it, in order to lower the proportion of possible surfactant in the PVDF below 300 ppm, this proportion being expressed with respect to the dried PVDF,
    • sodium acetate and optionally a potassium alkylsulphonate are added to the washed dispersion,
    • the dispersion from the preceding stage is dried by any means in order to recover the PVDF as a powder comprising the sodium acetate and optionally a potassium alkylsulphonate.
EP04290393A 2003-03-03 2004-02-13 Process for preparation of thermally stable PVDF Expired - Lifetime EP1454923B1 (en)

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FR0302532A FR2852017B1 (en) 2003-03-03 2003-03-03 PROCESS FOR PRODUCING THERMALLY STABLE PVDF
FR0302532 2003-03-03

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FR2852016B1 (en) * 2003-03-03 2006-07-07 Atofina PROCESS FOR PRODUCING THERMALLY STABLE PVDF
CN101437891B (en) * 2006-05-01 2012-02-29 阿科玛股份有限公司 Fluoropolymers having improved whiteness
WO2008005745A2 (en) * 2006-07-06 2008-01-10 Arkema Inc. Ultra-high molecular weight poly(vinylidene fluoride)
US20080027456A1 (en) * 2006-07-19 2008-01-31 Csaba Truckai Bone treatment systems and methods
US20080023398A1 (en) * 2006-07-28 2008-01-31 General Electric Company Method for removal and recovery of water from polymer manufacturing
EP2714789B1 (en) 2011-05-25 2016-02-03 Arkema, Inc. Irradiated fluoropolymer articles having low leachable fluoride ions
JP2013253141A (en) * 2012-06-05 2013-12-19 Kureha Corp Vinylidene fluoride-based polymer and method for producing the same
WO2015048697A1 (en) * 2013-09-30 2015-04-02 Arkema Inc. Heat stabilized polyvinylidene fluoride polymer composition
US12060463B2 (en) * 2018-11-22 2024-08-13 Solvay Specialty Polymers Italy S.P.A. Process for manufacturing heat treated PVDF
FR3142481A1 (en) 2022-11-29 2024-05-31 Arkema France PVDF-BASED PROTON EXCHANGE MEMBRANE

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GB1182680A (en) * 1966-12-12 1970-03-04 Daikin Ind Ltd Heat Stabilized Vinylidene Fluoride Polymer
FR2286153A1 (en) * 1974-09-24 1976-04-23 Ugine Kuhlmann POLYMERIZATION OR COPOLYMERIZATION PROCESS IN EMULSION OF VINYLIDENE FLUORIDE
US4569978A (en) * 1984-07-25 1986-02-11 Pennwalt Corporation Emulsion polymerization of vinylidene fluoride polymers in the presence of trichlorofluoromethane as chain transfer agent
FR2644466B1 (en) 1989-03-15 1992-08-14 Solvay PROCESS FOR THE MANUFACTURE OF VINYLIDENE FLUORIDE POLYMERS AND USE OF VINYLIDENE FLUORIDE POLYMERS FOR THE FORMULATION OF PAINTS
US5543259A (en) * 1993-12-13 1996-08-06 Xerox Corporation Developer compositions
US5955556A (en) * 1995-11-06 1999-09-21 Alliedsignal Inc. Method of manufacturing fluoropolymers
BE1010086A3 (en) * 1996-03-22 1997-12-02 Solvay Polymer fluoride compositions stabilised vinylidene heat.
IT1295535B1 (en) 1996-07-01 1999-05-12 Ausimont Spa VINYLIDENFLUORIDE (VDF) POLYMERIZATION PROCESS
US6689833B1 (en) 1997-04-09 2004-02-10 E. I. Du Pont De Nemours And Company Fluoropolymer stabilization
US6214251B1 (en) * 1999-03-09 2001-04-10 Hew-Der Wu Polymer electrolyte composition
US6462109B1 (en) * 1999-10-12 2002-10-08 Eastman Chemical Company Surfactantless latex compositions and methods of making polymer blends using these compositions
FR2804438A1 (en) * 2000-01-31 2001-08-03 Atofina Preparation of reduced-yellowing fluorinated polymer is carried out by aqueous emulsion polymerisation of vinylidene fluoride (and other monomers) using a lithium perfluoroalkanoate as surfactant
US6780935B2 (en) * 2000-02-15 2004-08-24 Atofina Chemicals, Inc. Fluoropolymer resins containing ionic or ionizable groups and products containing the same
FR2852016B1 (en) * 2003-03-03 2006-07-07 Atofina PROCESS FOR PRODUCING THERMALLY STABLE PVDF

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JP2004263190A (en) 2004-09-24
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US7045584B2 (en) 2006-05-16
DE602004002973T2 (en) 2007-07-05
DE602004002973D1 (en) 2006-12-14
FR2852017A1 (en) 2004-09-10
FR2852017B1 (en) 2005-04-22

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